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Abstract:
Nominally pure and Cu-doped (0.01, 0.1, and 1 wt% of copper oxide) PLZT 8/65/35 ceramics were investigated with regard to their ESR and optical spectra (absorption and luminescence). ESR investigations were performed at 4.2K ≤ T ≤ 300 K in the X and K bands both before and after annealing the samples in oxygen and hydrogen atmospheres. The observed spectra were shown to be a superposition of Cu2+ spectra in axial and cubic crystal fields. Cu2+ substitutes for Ti4+ and the excess charge can be compensated by La3+ on a nearest-neighbor site, thus creating axialsymmetry. The centers of cubic symmetry are those where the charge is compensated in distant spheres. In contrast to pure PLZT, PLZT:Cu exhibits a new luminescence band peaking at 1.18 eV. This emission is ascribed to the 2T2(D)→ 2E(D) transition of Cu2+(3d9) which can be excited either in the resonant 1.87 eV band or via charge-transfer excitation bands at 2.40, 2.57, and 3.03 eV. The absorption band at 1.45 eV is assumed to be that of Cu+ ions. Annealing in hydrogen and in oxygen atmospheres caused decrease and restoration, respectively, of the ESR and luminescence intensities as a consequence of Cu2+ conversion into Cu1+ and vice versa.
